A drill bit for use in a borehole at least partially containing drilling fluid includes a bit body having at least two bit components, including at least one leg, the leg having a journal segment, and a roller cone rotatably mounted upon the journal segment and forming at least one bearing cavity therebetween. Also included is an annular primary seal disposed between the leg and the roller cone, an annular secondary seal disposed between the leg and the roller cone and between the annular primary seal and the borehole and an annular space disposed between the annular primary seal and the annular secondary seal, the annular space at least partially containing fluid and being in substantially absolute fluid isolation from the bearing cavity and a conduit for permitting the flow of fluid from the annular space to the borehole. The annular secondary seal may be primarily elastomeric and the means for permitting the flow of fluid may further permit the flow of fluid from the borehole to the annular space. The annular space may at least partially include a grease possessing a water washout value of under approximately 50% per ASTM D-4049 water spray test for lubrication characteristics and the grease may include a polymer tackifier of between approximately 1% and approximately 5% by weight.

Claim:

What is claimed is:

1. A drill bit for use in a borehole comprising: a bit body having at least two bit components, said bit components including at least one leg, said leg having a journalsegment, said bit components further including a roller cone rotatably mounted upon said journal segment and forming at least one bearing cavity therebetween; an annular primary seal disposed between said leg and said roller cone and between saidbearing cavity and the borehole, said annular primary seal having a primarily dynamic sealing surface; an annular secondary seal disposed between said annular primary seal and the borehole, said annular secondary seal having a primarily dynamic sealingsurface; wherein a first contact pressure occurs at said primarily dynamic sealing surface of said annular primary seal and a second contact pressure occurs at said primarily dynamic sealing surface of said annular secondary seal, said first contactpressure being greater than said second contact pressure; to allow fluid migration past said annular secondary seal and an annular space disposed between said annular primary seal and said annular secondary seal, said annular space at least partiallycontaining fluid and in substantially absolute fluid isolation from said bearing cavity.

7. The drill bit of claim 1 wherein said annular secondary seal is disposed in an annular groove formed in one of said bit components.

8. A drill bit for use in a borehole at least partially containing drilling fluid, comprising: a bit body having at least two bit components, said bit components including at least one leg, said leg having a journal segment, said bit componentsfurther including a roller cone rotatably mounted upon said journal segment and forming at least one bearing cavity therebetween; an annular primary seal disposed between said leg and said roller cone; an annular secondary seal disposed between saidleg and said roller cone and between said annular primary seal and the borehole, said annular secondary seal having a primarily dynamic sealing surface and a primarily static sealing surface, wherein a first contact pressure occurs at said primarilydynamic sealing surface and a second contact pressure occurs at said primarily static sealing surface, said first contact pressure and said second contact pressure being unequal to allow fluid migration past said annular secondary seal; and an annularspace disposed between said annular primary seal and said annular secondary seal, said annular space at least partially containing fluid and in substantially absolute fluid isolation from said bearing cavity.

9. The drill bit of claim 8 wherein said first contact pressure is greater than said second contact pressure.

10. The drill bit of claim 8 wherein said second contact pressure is greater than said first contact pressure.

11. A drill bit for use in a borehole at least partially containing drilling fluid, comprising: a bit body having at least two bit components, said bit components including at least one leg, said leg having a journal segment, said bit componentsfurther including a roller cone rotatably mounted upon said journal segment and forming at least one bearing cavity therebetween; an annular primary seal disposed between said leg and said roller cone; and an annular secondary seal disposed betweensaid annular primary seal and the borehole and between said leg and said roller cone, wherein said annular secondary seal is engageable with said leg and said roller cone, said annular secondary seal including a sealing surface engageable with one ofsaid bit components, wherein said sealing surface includes first and second regions; and wherein a first contact pressure occurs at said first region of said sealing surface and a second contact pressure occurs at said second region of said sealingsurface, said first contact pressure being greater than said second contact pressure to allow fluid migration past said annular secondary seal.

12. The drill bit of claim 11 further including an annular space disposed between said annular primary seal and said annular secondary seal, said annular space at least partially containing fluid and in substantially absolute fluid isolationfrom said bearing cavity.

13. The drill bit of claim 12 wherein said fluid in said annular space is capable of migrating past said annular secondary seal from said annular space to the borehole.

The present invention relates generally to sealed bearing earth boring drill bits, such as rotary cone rock bits. More particularly, the invention relates to drill bits that have a dual seal arrangement for protecting internal bearing elements. Yet more particularly, the present invention relates to providing for pressure communication between the interior and exterior of earth boring dual-seal drill bits.

During earthen drilling operations with the use of sealed bearing drill bits, such as rotary cone drill bits, it is necessary to protect the bearing elements of the bit from contamination in order to sustain bit operability. In particular, it isdesirable to isolate and protect the bearing elements of the bit, such as bearings, bearing lubricant and bearing surfaces that are located in a bearing cavity or cavities between each corresponding bit leg and roller cone, from earthen cuttings, mud andother debris in the drilling environment. Introduction into the bearing system of such contaminants can lead to deterioration of the bearing lubricant, bearings and bearing surfaces, causing premature bit failure. It is well known in the art to providean annular seal around the bearing elements to prevent contamination thereof by particles entering through the annular opening and into the gap that is formed between each leg and corresponding roller cone and that extends to the bearing cavity.

In a downhole drilling environment, the borehole contains "drilling fluid," which can be drilling mud, other liquids, air, other gases, or a mixture or combination thereof. In the typical liquid drilling environment of a petroleum well, thedownhole fluid pressure at the location of the drill bit, the "external pressure," can be very high and fluctuating. At the same time, internal pressure within the bearing cavity, the "internal pressure," can also be very high and fluctuating due, forexample, to thermal expansion and out-gassing of lubricant in the bearing cavity, and cone movement relative to the leg. These high pressure changes internal and external to the bearing cavity may cause a differential pressure across the bearing seal,thus resulting in a major load on the seal. When the internal pressure is greater than the external pressure, the seal may be drawn to and possibly extruded into the gap. Likewise, a greater external pressure can cause the seal to be drawn in thedirection of the bearing cavity and possibly extruded therein. This may cause excessive wear to the seal and eventual bit inoperability. Furthermore, when the pressure differential reaches a certain level in each above scenario, the seal can leak,allowing lubricant to pass from the bearing cavity into the gap in the first scenario, and drilling fluid to pass from the gap into the bearing cavity in the second scenario.

Generally, when the internal pressure and the external pressure are equal, the differential pressure across the bearing cavity seal will be zero. There will be no pressure to force the drilling fluid or lubricant by the seal, or to force theseal into the gap or bearing cavity. Thus, it is generally desirable to achieve or maintain a differential pressure of approximately zero. In the prior art, a lubricant reservoir system having a flexible diaphragm located in a lubricant reservoircavity in the bit leg is used to equalize the internal and external pressure. The flexible diaphragm separates the internal lubricant from the external drilling fluid and communicates the external pressure to the portion of the bearing seal adjacent tothe bearing cavity. This type of pressure compensation system for a single seal bit is schematically shown in FIG. 1a.

Referring to FIG. 1a, when the external, or borehole, pressure Pd of the drilling fluid in the borehole B, increases and is greater than the internal pressure Pg in the bearing cavity, the seal S.sub.1 will be forced inwardly toward the bearingcavity B.sub.2. With the use of a flexible diaphragm D.sub.1 the external pressure Pd is also applied to the diaphragm D.sub.1, which transmits the pressure Pd, equalizing it with the internal pressure Pg. As a result, the pressure on both sides of theseal S.sub.1 is balanced, preventing the occurrence of any differential pressure across the seal S.sub.1. Similarly, when the pressure Pg increases, Pg will temporarily be larger than Pd, causing the diaphragm D.sub.1 to expand outwardly to increase theinternal volume of the bearing cavity B.sub.2. As the internal volume increases, the internal pressure Pg will decrease. Pg will drop to equilibrium with Pd, and the internal volume will stop increasing.

Dual seal arrangements have been proposed having an outer seal around a primary inner seal. The purpose of including a second seal is typically to provide a second layer of protection from particles entering the gap through the annular opening. When an outer seal is added, it may be necessary, such as in drill bits used for petroleum wells, that the bit be capable of compensating for the differential pressure across both seals. FIG. 1b shows a two-seal schematic with both seals providingsubstantially absolute seals, the "space" Sp formed between the seals S.sub.1, S.sub.2 being completely filled with incompressible fluid, and there being no variation in the density of the incompressible fluid. In this scenario, the incompressible fluidin space S.sub.p between the seals S.sub.1, S.sub.2 acts like a rigid body that transmits pressure from Pg.sub.1, which is the (internal) bearing cavity pressure, to Pd and from Pd to Pg.sub.1. For example, when the external fluid pressure Pd increases,diaphragm D.sub.1 will be pushed inwardly, causing the internal pressure Pg.sub.1 to equal the external pressure Pd. Because the fluid between seals S.sub.1 and S.sub.2 is incompressible, it will transmit the increased pressure between S.sub.1 andS.sub.2 and neither seal S.sub.1 or S.sub.2 will be displaced.

However, during borehole drilling operations, such as with rotary cone sealed bearing drill bits, various factors will alter ideal conditions and require something more to equalize the differential pressure across both seals S.sub.1 and S.sub.2. For example, there is relative movement between the roller cone and bit leg, which causes the volume of the space S.sub.p between the seals S.sub.1 and S.sub.2 to significantly increase and decrease. A change in the volume of the space Sp will changethe chamber pressure Pg.sub.2 in the space Sp, causing conditions where Pg.sub.2 >Pd, Pg.sub.1 upon contraction of the space Sp, and where Pg.sub.2 <Pd, Pg.sub.1 upon expansion of the space Sp. Thus, there will be differential pressures acrossboth seals S.sub.1, S.sub.2, causing their movement and possible extrusion, which can cause accelerated seal wear and eventual bit failure.

Another potential factor altering ideal conditions is the thermal expansion, or out-gassing, of the incompressible fluid between the seals S.sub.1, S.sub.2 due to elevated temperatures within the bit. Referring to FIG. 1b, expansion of theincompressible fluid in the space Sp between the seals S.sub.1, S.sub.2 will elevate the chamber pressure Pg.sub.2. Increasing the chamber pressure Pg.sub.2 can cause a differential pressure across the seals S.sub.1, S.sub.2 such that Pg.sub.2 >Pd,Pg.sub.1, which can result in accelerated wear and possible extrusion of seals S.sub.1, S.sub.2. Still another factor is the existence of air trapped in the space Sp between the seals S.sub.1, S.sub.2. In this instance, the mixture of air and fluid inspace Sp is not incompressible. When external pressure Pd increases, Pg.sub.1 will eventually equal Pd due to the diaphragm D.sub.1, but Pd >Pg.sub.2 and Pg.sub.1 >Pg.sub.2 because of the presence of air in the space Sp between the seals S.sub.1,S.sub.2. The chamber pressure Pg.sub.2 in the space Sp will not increase until the seals S.sub.1, S.sub.2 move closer together and the air volume in space Sp decreases. This differential pressure across seals S.sub.1, S.sub.2 will cause the movementand possible extrusion of the seals into the space Sp and excessive wear on the seals.

In the prior art, U.S. Pat. No. 5,441,120, which is hereby incorporated by reference herein in its entirety, discloses the use of an additional flexible diaphragm D.sub.2, such as shown in FIG. 1c herein, to attempt to equalize, or balance thechamber pressure Pg.sub.2 of the space Sp with the external pressure Pd or internal pressure Pg.sub.1. Further increases in external pressure Pd will thereafter be transmitted through the fluid in the space Sp. Such a system has various disadvantages. For example, a system made in accordance with U.S. Pat. No. 5,441,120 requires or occupies much space within the bit leg, structurally weakening the bit. For another example, such a system does not allow for pressure relief from the space Sp, such ascaused by thermal expansion and outgassing of the incompressible fluid between the seals S.sub.1, S.sub.2, which can cause damage to the seals as described above. It should be understood that there are other disadvantages and features of the disclosureof U.S. Pat. No. 5,441,120 as well as various features of the invention of each claim herein that distinguish one from the other. Thus, in any comparison, the disclosure of U.S. Pat. No. 5,441,120 should be compared as a whole to the claimedinvention of any particular claim herein as a whole to distinguish them.

U.S. Pat. Nos. 4,981,182 and 5,027,911, which are also hereby incorporated herein in their entireties, disclose various embodiments of drill bits including inner and outer seals and where lubricant is bled out of the bit past the outer seal toprevent drilling debris from accumulating and damaging the inner and outer seals. In some such embodiments, passages in the bit allow lubricant to travel from the bearing cavity to the space between the seals. In other embodiments, a hydrodynamic innerseal is used, which allows the leakage of lubricant from the bearing cavity to the space between the seals. In both instances, the pressure of the lubricant presumably forces the outer seal to open and allow the bleeding of lubricant from the bit. These systems also have various disadvantages. For example, the continuous bleeding of lubricant past the outer seal (particularly if the outer seal fails) can lead to the depletion of bearing lubricant in the bit, and cause bearing and bit damage dueto a lack of lubricant. For another example, if the space between the seals in such configurations is not filled with lubricant, such as which will occur if there is a decrease or stoppage in the flow of lubricant from the bearing cavity to the space, ahigh pressure differential across the seals can result, causing damage to the seals as described above. For yet another example, with many such embodiments, because the space between the seals and the bearing cavity are in fluid communication, thereexists the possibility that debris or drilling fluid bypassing the outer seal, such as when the outer seal fails, will move through the space between the seals and into the bearing cavity, causing contamination and damage to therein and to the bearingelements. It should be understood that there are other disadvantages and features of the disclosures of U.S. Pat. Nos. 4,981,182 and 5,027,911 as well as various features of the invention of each claim herein that distinguish them. Thus, in anycomparison of U.S. Pat. No. 4,981,182 or 5,027,911 and any claim herein, such disclosure should be compared as a whole to the claim as a whole to distinguish them.

Thus, there remains a need for improved techniques and mechanisms for substantially balancing or minimizing the pressure differential upon the primary and secondary seals of a dual seal configuration, particularly by allowing pressurecommunication between the interior and exterior of the drill bit. Ideally, the devices and techniques will accommodate cone movement, thermal expansion of the fluid and/or out-gassing between the primary and secondary seals, and trapped air in the spacebetween the seals. Especially well received would be pressure communication devices that do not require substantial additional components, large space requirements in the bit, or highly complex manufacturing requirements for the bit. Also well receivedwould be a pressure communication technique and device that will prevent the pressure differential across the dual seals from exceeding an upper limit, such as, for example, 100 psi. It would also be advantageous to include the use of an incompressiblefluid having the capabilities of retaining sufficient viscosity to act as a medium for the transmission of energy between the primary and secondary seals, of retaining its lubrication properties, and/or of slowing the intrusion of abrasive particles tothe primary seal--when and after the incompressible fluid is exposed to drilling fluid. These and other needs in the art will become apparent to those of skill in the art upon review of this patent specification, claims and drawings.

BRIEF SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided techniques, methods and apparatuses for communicating fluid pressure between a borehole and the space between the seals of a dual-seal drill bit. The invention includes a drill bit foruse in a borehole at least partially containing drilling fluid, including a bit body having at least two bit components, the bit components including at least one leg, the leg having a journal segment, the bit components further including a roller conerotatably mounted upon the journal segment and forming at least one bearing cavity therebetween. The drill bit also includes an annular primary seal disposed between the leg and the roller cone and an annular secondary seal disposed between the leg andthe roller cone and between the annular primary seal and the borehole. The annular secondary seal may be primarily elastomeric, may be primarily axially or radially energized, and/or may be disposed in an annular groove formed in one of the bitcomponents or an annular interstice formed between the leg and the roller cone.

An annular space is disposed between the annular primary seal and the annular secondary seal. The annular space may at least partially contain fluid and may be in substantially absolute fluid isolation from the bearing cavity. The annular spacemay at least partially include a grease possessing a water washout value of under approximately 50% per ASTM D-4049 water spray test for lubrication characteristics, the grease including a polymer tackifier of between approximately 1% and approximately5% by weight.

In one aspect of the invention, there is include means for permitting the flow 6f fluid from the annular space to the borehole. The drill bit can be configured such that the means further permits the flow of fluid from the borehole to theannular space. The means can be integral with the annular secondary seal, integral with at least one of the bit components or a combination thereof.

In another aspect of the invention, a first contact pressure occurs at the primarily dynamic sealing surface of the annular primary seal and a second contact pressure occurs at the primarily dynamic sealing surface of the annular secondary seal,the first contact pressure being greater than the second contact pressure. In yet another aspect of the invention, the annular secondary seal includes a primarily dynamic sealing surface and a primarily static sealing surface, wherein a first contactpressure occurs at the primarily dynamic sealing surface and a second contact pressure occurs at the primarily static sealing surface, the first contact pressure and the second contact pressure being unequal. In still another aspect of the invention,the annular secondary seal includes a sealing surface engageable with one of the bit components, wherein the sealing surface includes first and second regions. A first contact pressure occurs at the first region of the sealing surface and a secondcontact pressure occurs at the second region of the sealing surface, the first contact pressure being greater than the second contact pressure.

In accordance with another aspect of the invention, the annular space has a chamber pressure which may be altered by allowing the passage of fluid from the annular space to the borehole and from the borehole to the annular space. In a variationof this aspect, when a differential pressure occurs between the chamber pressure and the borehole pressure, the chamber pressure may be altered when the differential pressure is between approximately 0 psi and approximately 100 psi; and, in anothervariation, between approximately 30 psi and approximately 70 psi.

In another aspect of the invention, the bit may be designed so that fluid migrates from the annular space to the borehole when the chamber pressure is greater than the borehole pressure. The bit may be further designed so that fluid migratesfrom the borehole to the annular space when the borehole pressure is greater than the chamber pressure. In another aspect, the annular secondary seal includes first and second side surfaces adjacent to the sealing surface, and at least one of the bitcomponents includes at least one non-energizing surface at least partially engageable with one of the first and second side surfaces of the annular secondary seal. The non-energizing surface of the bit component includes first and second regions, thefirst region of the non-energizing surface being uneven with respect to the second region of the non-energizing surface. Further, the first region of the non-energizing surface may include at least one surface feature.

In still another aspect of the invention, the annular secondary has a sealing surface engageable with at least one bit component, the sealing surface having first and second adjacent regions, wherein the thickness of the annular secondary seal atthe first region of the sealing surface is greater than the thickness of the annular secondary seal at the second region of the sealing surface. In yet another aspect, the annular secondary seal includes at least one region having a taperedcross-section, or the cross-section of the entire annular secondary seal is tapered. Still, a further aspect of the invention includes an annular secondary seal including at least one region having an at least partially non-symmetrical cross-section.

In another aspect, the annular secondary seal including at least first and second circumferentially adjacent regions, a primarily static sealing surface and a primarily dynamic sealing surface. Each of the first and second circumferentiallyadjacent regions has a height measured between the primarily static and primarily dynamic sealing surfaces. Further, at least one of the static and dynamic sealing surfaces is at least partially disposed on the first and second circumferentiallyadjacent regions, the height of the first circumferentially adjacent region being greater than the height of the second circumferentially adjacent region.

In another aspect, at least one of the bit components includes an annular groove having first and second circumferentially adjacent regions, wherein the width of the first circumferentially adjacent region is greater than the width of the secondcircumferentially adjacent region and the annular secondary seal is disposed within the annular groove. In still another aspect, the bit components include first and second primarily non-energizing seal engagement surfaces and the annular secondary sealhas first and second sides engageable with the first and second primarily non-energizing seal engagement surfaces of the bit components, respectively. At least one of the first and second primarily non-energizing seal engagement surfaces of the bitcomponents includes first and second regions, the first region including at least one cut-out.

In accordance with one aspect of the present invention, the bit components include first and second primarily non-energizing seal engagement surfaces and the annular secondary seal having first and second sides engageable with the first andsecond primarily non-energizing seal engagement surfaces of the bit components, respectively. At least one of the first and second primarily non-energizing seal engagement surfaces of the bit components includes first and second regions, the firstregion being uneven with respect to the second region.

In another aspect, at least one of the bit components includes an annular groove and the annular secondary seal has first and second sides and being disposed within the annular groove. The annular groove includes a first primarily non-energizingsurface engageable with the first side of the annular secondary seal and a second primarily non-energizing surface engageable with the second side of the annular secondary seal, the first primarily non-energizing surface disposed between the secondprimarily non-energizing surface and the bearing cavity. Further, the second primarily non-energizing surface includes at least first and second circumferentially adjacent regions, the first region of the second primarily non-energizing surfaceincluding at least one cut-out, whereby the distance from the first region of the second primarily non-energizing surface to the first primarily non-energizing surface is greater than the distance from the second region of the second primarilynon-energizing surface to the first primarily non-energizing surface.

In still a further aspect of the invention, the annular secondary seal includes first and second circumferentially adjacent regions and a sealing surface extending at least partially upon the first and second circumferentially adjacent regions,wherein the sealing surface of the first circumferentially adjacent region is uneven with respect to the sealing surface of the second circumferentially adjacent region.

In still a further aspect, the leg and roller cone each include at least one component surface engageable with the annular secondary seal, at least one such component surface including first and second adjacent regions, wherein the first regionof the component surface is uneven with respect to the second region of the component surface. In still another aspect, at least one of the bit components includes an annular groove having at least first and second circumferentially adjacent regions,the depth of the first circumferentially adjacent region being greater than the depth of the circumferentially adjacent second region and the annular secondary seal being disposed within the annular groove. Another aspect includes an annular intersticeformed between the bit components, the annular interstice having at least one seal engagement surface, the seal engagement surface having first and second circumferentially adjacent regions. The depth of the first circumferentially adjacent region ofthe seal engagement surface is greater than the depth of the second circumferentially adjacent region and the annular secondary seal is disposed within the annular interstice.

In accordance with another aspect of the present invention, the annular secondary seal includes a primarily dynamic sealing surface and a primarily static sealing surface, each of the primarily dynamic and static sealing surfaces engageable withone of the bit components. At least a portion of at least one of the primarily dynamic and static sealing surfaces includes a non-elastomeric porous inlay capable of at least partially allowing the passage of fluid past the annular secondary seal whenthe portion of at least one of the sealing surfaces is engaged with the bit component.

In still a further aspect, the drill bit has an opening in the exterior surface of the leg and a passage disposed in the leg and extending from the opening to the annular space, the passage allowing fluid communication between the annular spaceand the borehole. In a variation of this aspect, a plurality of passages may be disposed in the leg and extend from the opening to the annular space. The passage may be capable of allowing the flow of fluid from the annular space to the borehole andfrom the borehole to the annular space. A fluid control member may be disposed in the leg in fluid communication with the passage. The fluid control member may be a two-way valve, or a primarily one-way fluid valve capable of allowing the flow of fluidfrom the annular space to the borehole. The annular space may be filled with incompressible fluid through the passage. The annular space may be at least partially includes a grease possessing a water washout value of under approximately 50% per ASTMD-4049 water spray test for lubrication characteristics, the grease including a polymer tackifier of between approximately 1% and approximately 5% by weight.

In another aspect the annular primary seal may form a substantially absolute seal and the annular space in substantially absolute fluid isolation from the bearing cavity. An opening is disposed in the exterior surface of the leg and a passage isdisposed in the leg and extending from the opening to the annular space. The passage is filled with incompressible fluid and a plug is disposed in the opening.

Another aspect of the invention involves at least one of the bit components including at least two seal engagement surfaces, the annular secondary seal including a primarily dynamic sealing surface and a primarily static sealing surface, each thesealing surface of the annular secondary seal having a width and being engageable at the width with one of the seal engagement surfaces of the bit components. At least one of the annular primarily dynamic and primarily static sealing surfaces includesfirst and second regions, the width of the first region being smaller than the width of the second region.

Still, a further aspect of the invention includes an incompressible fluid for use to lubricate a seal in a sealed bearing drill bit, the drill bit useful in a borehole at least partially containing drilling fluid and solid particles, including agrease capable of lubricating at least one seal after the grease contacts drilling fluid. The grease may further capable of trapping solid particles to assist in preventing the ingress of solid particles to the seal, and/or transmitting energy betweenfirst and second seals after the grease contacts drilling fluid. The grease may be disposed between a primary seal and a secondary seal. The grease may possess a water washout value of under approximately 50% per ASTM D-4049 water spray test forlubrication characteristics. 30% per ASTM D-4049 water spray test for lubrication characteristics, and/or a polymer tackifier of between approximately 1% and approximately 5% by weight. The grease may include between approximately 10 percent andapproximately 30 percent by weight of at least one mineral oil and between approximately 70 percent and approximately 90 percent by weight of at least one synthetic oil, and/or between approximately 1.0 percent and approximately 10.0 percent by weight ofsilica thickener and between approximately 1.0 percent and approximately 5.0 percent by weight of tackifier.

Accordingly, the present inventions comprise various combinations of features and advantages which enable it to substantially advance the technology associated with dual-seal pressure communication techniques and apparatuses. Each of theseaspects of the invention, which may be used alone or in a combination with others, provides an improved technique and mechanism for substantially balancing or minimizing the pressure differential upon the primary and secondary seals of a dual sealconfiguration, particularly by allowing pressure communication between the interior and exterior of the drill bit. The present invention includes devices that accommodate cone movement, thermal expansion of the fluid and/or out-gassing between theprimary and secondary seals, and trapped air in the space between the seals. Many of the pressure communication devices of the present invention do not require substantial additional components, large space requirements in the bit, or highly complexmanufacturing requirements for the bit. Also included are various pressure communication techniques and devices that will prevent the pressure differential across the dual seals from exceeding an upper limit, such as, for example, 100 psi. Yet afurther feature of many aspects of the invention involves the use of an incompressible fluid having the capabilities of retaining sufficient viscosity to act as a medium for the transmission of energy between the primary and secondary seals, of retainingits lubrication properties, and/or of slowing the intrusion of abrasive particles to the primary seal--when and after the incompressible fluid is exposed to drilling fluid.

The characteristics and advantages of various aspects and embodiments of the present invention described herein, as well as additional features and benefits, will be readily apparent to those skilled in the art upon reading the following detaileddescription, referring to the accompanying drawings and reading the appended claims.

It should be understood that each claim herein does not necessarily require or encompass more than one feature or aspect of the present invention. Further, the disadvantages of the prior art and advantages, features and aspects of the presentinvention should not be considered limitations to any of the appended claims unless expressly recited therein, each claim being construed independently.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of preferred embodiments of the invention, reference will now be made to the accompanying drawings wherein:

FIG. 1a is a schematic of a prior art single seal drill bit pressure compensation system.

FIG. 3 is a cross-sectional view of one leg and cone of the rotary cone drill bit of FIG. 2.

FIG. 4 is a is a partial cross-sectional view of one leg and cone of a rotary cone drill bit employing a primary seal disposed in an annular groove formed in a leg journal and a secondary seal disposed in an annular groove formed in the cone.

FIG. 5 is a partial cross-sectional view of one leg and cone of a rotary cone drill bit employing a primary elongated O-ring seal disposed in a groove in the roller cone and a radially energized secondary O-ring seal disposed in a groove in theleg journal segment.

FIG. 6 is a partial cross-sectional view of one leg and cone of a rotary cone drill bit employing a primary O-ring seal disposed in a groove in the roller cone and a secondary O-ring seal disposed in a groove formed in the leg backface surface.

FIG. 7 is a partial cross-sectional view of one leg and cone of a rotary cone drill bit of another embodiment employing a primary seal disposed in an interstice and a secondary seal disposed in a groove in the roller cone.

FIG. 8 is a partial cross-sectional view of one leg of a rotary cone drill bit of another embodiment employing a primary elongated O-ring seal disposed in a groove in the roller cone and a secondary O-ring seal disposed in an interstice, andhaving a passage extending from the annular space between the seals and the exterior of the bit.

FIG. 9 is a partial cross-sectional view of another embodiment employing a primary O-ring seal disposed in an interstice and a secondary seal disposed in a groove in roller cone.

FIG. 12 is a partial cross-sectional view of a drill bit leg and cone of another embodiment employing a radially energized O-ring secondary seal.

FIG. 13 is a partial cross-sectional view of a drill bit leg and cone of another embodiment employing a primary O-ring seal disposed in a groove in the roller cone and a secondary elongated O-ring seal disposed in a groove in the roller cone.

FIG. 14 is an exploded partial cross-sectional view of a drill bit leg and cone of an embodiment employing a primary O-ring seal in an interstice and a secondary elongated O-ring seal disposed in a groove in the roller cone.

FIG. 15 is an exploded partial cross-sectional view of a drill bit leg and cone of an embodiment employing a secondary elongated O-ring seal disposed in a groove in the roller cone.

FIG. 16 is a partial cross-sectional view of a drill bit leg of another embodiment employing a primary O-ring seal disposed in an interstice and a secondary seal disposed in a groove in the leg journal segment.

FIG. 17 is a partial cross-sectional view of a drill bit leg and cone of an embodiment of the present invention employing a secondary seal having a thin region and capable of allowing two-way migration of fluid past the secondary seal.

FIG. 17a is a top plan view of the secondary seal of FIG. 17.

FIG. 17b is a cross-sectional view of the secondary seal of FIG. 17a taken along line 17b--17b.

FIG. 17c is an exploded partial cross-sectional view of another embodiment of the secondary seal having a decreased thickness, bellows shaped, region capable of allowing two-way fluid migration.

FIG. 18 is a partial cross-sectional view of another embodiment of the present invention employing a secondary seal having a tapered region formed along the dynamic sealing surface of the secondary seal.

FIG. 19 is a partial cross-sectional view of another embodiment of the present invention employing a secondary seal having a tapered region formed along the static sealing surface of the secondary seal.

FIG. 20 is a partial cross-sectional view of another embodiment of the present invention employing a secondary seal having a decreased height region.

FIG. 20a is a top plan view of the secondary seal of FIG. 20.

FIG. 20b is a partial top plan view of another embodiment of the secondary seal having a decreased height region.

FIG. 20c is a cross-sectional view of the seal of FIG. 20a taken along line 20c--20c.

FIG. 20d is a cross-sectional view of the seal of FIG. 20a taken along line 20d--20d.

FIG. 21 is a partial cross-sectional view of another embodiment of the present invention employing a secondary seal disposed in a groove having wide portions.

FIG. 21a is a partial plan view of a secondary seal disposed in a groove having wide portions.

FIG. 21b is a partial cross sectional view of the embodiment of FIG. 21a taken along line 21b--21b.

FIG. 22 is an embodiment of the present invention of a secondary seal having fluid leakage depressions in the dynamic sealing surface.

FIG. 22a is a partial cross sectional view of the embodiment of FIG. 22 taken along line 22a--22a.

FIG. 23 is another embodiment of the present invention of a secondary seal having fluid leakage depressions in the static sealing surface.

FIG. 24 is another embodiment of the present invention of a secondary seal having fluid leakage depressions in the dynamic sealing surface.

FIG. 25 is a partial cross-sectional view of an embodiment of the present invention employing a secondary seal disposed in a groove having a deep region.

FIG. 25a is a partial plan view of a secondary seal disposed in a groove having a deep region.

FIG. 25b is a partial cross sectional view of the embodiment of FIG. 25a taken along line 25b--25b.

FIG. 26 is an embodiment of the present invention of a secondary seal having a porous inlay.

FIG. 26a is a partial cross sectional view of the embodiment of FIG. 26 taken along line 26a--26a.

FIG. 27 is a partial cross-sectional view of an embodiment of the present invention employing a conduit extending from the space between the seals to the bit exterior and a fluid control member.

FIG. 27a is a bottom view of the washer of the fluid control member FIG. 27.

FIG. 27b is a partial isolated view of another embodiment of a fluid control member.

FIG. 27c is a partial isolated view of a conduit extending from the space between the seals to the bit exterior.

FIG. 28 is a partial cross-sectional view of an embodiment of the present invention employing a secondary seal disposed in a groove having wide region.

FIG. 28a is a partial plan view of a secondary seal disposed in a groove having a wide region.

FIG. 28b is a partial cross sectional view of the embodiment of FIG. 28a taken along lines 28b--28b.

FIG. 29 is a partial cross-sectional view of an embodiment of the present invention having a modified secondary seal with a non-symmetrical dynamic sealing surface.

FIG. 30 is a partial cross-sectional view of an embodiment of the present invention having a conduit extending from the space between the seals to the bit exterior and a substantially one-way fluid valve.

DETAILED DESCRIPTION OF PREFERREDEMBODIMENTS

Presently preferred embodiments of the invention are shown in the above-identified figures and described in detail below. In illustrating and describing the preferred embodiments, like or identical reference numerals are used to identify commonor similar elements. The figures are not necessarily to scale and certain features and certain views of the figures may be shown exaggerated in scale or in schematic in the interest of clarity and conciseness.

Dual-seal drill bits are disclosed, for example, in U.S. patent application Ser. Nos. 08/982,081 entitled "Sealed Bearing Drill Bit with Dual-Seal Configuration," and Ser. No. 08/980,917 entitled "Composite Earth Boring Bit and Seal," both ofwhich have a common assignee as the present application and are hereby incorporated herein by reference in their entireties. Referring initially to FIGS. 2 and 3, a sealed-bearing earth boring rotary cone rock bit 10 is shown in an earthen annulus, orborehole 17. It should be understood that the present invention is not limited to rotary cone rock bits 10 for petroleum well drilling, but may similarly be used in other types of sealed bearing earth boring drill bits. The bit 10 includes a bit body12, a threaded pin end 14 and a cutting end 16. Legs 20 extend from bit body 12 toward the cutting end 16 of the bit 10. At the cutting end 16, each leg 20 carries a roller cone 18. Typically, rotary cone drill bits have three legs 20 and cones 18,although the present invention may be used in bits 10 with any number of leg 20/cone 18 combinations.

It should be understood that the following description is made, in part, with reference to a single leg 20, cone 18 and corresponding features, but applies equally to each leg 20 and cone 18 of the bit 10. Referring to FIGS. 3 and 4, the rollercone 18 is rotatably mounted upon a journal segment 23 of the leg 20, the journal segment 23 extending into the bore 73 of the cone 18. The journal segment 23 has a central axis 23a. The cone 18 is disposed on the leg 20 adjacent to a shirttail portion21 of the leg 20. Adjacent cone and leg backface surfaces 32, 22 form a gap 50 that extends between the leg 20 and cone 18 to the exterior 49 of the bit 10. The gap 50 exits the bit 10 to the borehole 17 at an annular opening 74. Preferably, the bitis configured with the gap 50 having a generally uniform width 51, although a uniform width 51 is not necessary for operation of the invention.

Still referring to FIGS. 3 and 4, a conventional drill bit bearing system 15, such as the roller bearing system disclosed in U.S. Pat. No. 5,793,719 to Crockett et al., which is incorporated herein by reference in its entirety, permits therotation of the cone 18 about the journal segment 23 during drilling operations. The conventional bearing system 15 includes various bearing elements. For example, the roller bearing system 15a of FIG. 4 includes cone bearing surfaces 34, journalbearing surfaces 35, roller bearings 25 and locking balls 27, disposed in one or more bearing cavities 75 formed between the cone 18 and journal 23, or in the bore 73 of the cone 18. A lubricant, such as grease (not shown), is provided to the bearingsystem 15 via a conventional lubricant reservoir system 30. A friction bearing system 15b (FIG. 5), operating as known in the art and having components, such as friction bearings 25a, similarly contained in the bearing cavities 75, may be used with thepresent invention. It should be understood that the present invention does not require a bearing system of any particular type.

Still referring to FIG. 3, a plenum 13 is shown formed in the bit body 12 in communication with the pin end 14 of the bit 10 allowing the supply of circulation fluid to one or more nozzles 28 (FIG. 2), as is known in the art. A circulationfluid, such as air, water, drilling mud or other fluids as is or become known in the art, is provided into the bit 10 from a fluid supply source (not shown) and through a supply conduit, such as a drill pipe (not shown), that is attached to the pin end14 of the bit 10, as also known in the art. The nozzles 28 (FIG. 2) operate to direct pressurized fluid against the bottom 70 of the borehole 17 to lift earthen cuttings and other debris up through the borehole 17 to the surface (not shown). Thenozzles 28 also direct the circulation fluid over the exterior 76 of the cones 18 and cutters 19 to free debris accumulating thereabout. However, the inclusion of a plenum 13, nozzles 28 are the supply of circulation fluid into the bit 10 is notrequired for the present invention.

The existence of earthen cuttings, mud and other debris in the borehole or annulus 17, along with "drilling fluid," which may be drilling mud, other liquids, gases or a combination thereof, and throughout the drilling environment makes itnecessary that the bearing system 15 be isolated therefrom, or sealed. Introduction into the bearing system 15 of such contaminants leads to deterioration of the lubricant and bearing system elements in the bearing cavity 75, such as, for example, theroller bearings 25 and bearing surfaces 34, 35 (FIG. 4) which, in turn, leads to premature bit failure. A bearing system seal arrangement 29 is included to seal the bearing cavity 75 to protect its contents, such as bearing system 15, thus assisting insustaining operability of the bit 10. A seal arrangement 29, as shown, for example, in FIG. 4, includes an annular primary seal 38 and an annular secondary seal 52.

Referring to FIG. 4, the seals 38, 52 must be able to function between a cone 18 and a leg 20 experiencing misalignment and relative movement during drilling operations due to flexing of the leg journal segment 23 and end-play, or cocking, of thecone 18 as a result of the uneven forces placed upon the cone exterior 76. Another consideration in configuring the seal arrangement 29 is the space within the bit 10 available for, or occupied by, the seal arrangement 29. The less space in the bit 10that is occupied by the seal arrangement 29, the more space is available for other elements of the bit 10, such as the bearing system 15, particularly the bearings, and the greater the resulting capacity of the bearing system 15 and operability of thebit 10. Yet another concern is to minimize the time, effort and machinery for manufacturing and assembling the bit 10, such as for machining the leg 20, journal segment 23 and cone 18.

Still referring to FIG. 4, although the present invention is not limited to any particular configuration of dual-seal arrangement, the annular primary seal 38 is preferably disposed between the bearing cavities 75 and the opening 74 and betweenthe cone 18 and journal segment 23, generally capable of providing an absolute seal around the bearing cavities 75. The term "absolute seal" as used herein means an intended fluid tight seal that allows no, or substantially no, fluid passage, by a sealhaving normal wear and tear and operating under typical pressure conditions, but which may yield to, some degree of minimal leakage, such as when the seal is operating with a differential pressure present. An example of a seal that does not provide anabsolute seal is a "hydrodynamic" seal, which allows fluid passage from the bearing cavity 75 to the gap 50. The annular secondary seal 52 is disposed between the primary seal 38 and the opening 74, and is generally capable of preventing substantialingress of large debris and particles from the exterior 49 of the bit 10 and gap 50 to the primary seal 38. The secondary seal 52 may be placed between the cone 18 and either the leg 20 (FIG. 6) or leg journal segment 23 (FIG. 4).

Referring to FIG. 4, as used herein, the term "bit components" includes, but is not limited to, the leg 20 having a leg journal segment 23, and the cone 18. Because the cone 18 rotates relative to the leg 20 and leg journal segment 23 duringdrilling operations, each seal 38, 52 is capable of providing a seal between bit components that move relative to one another. Sealing by seals 38, 52 is effected by compression, or energization, of the seal between an opposed pair of surfaces("energizing surfaces"), each energizing surface being on a different bit component. The remaining bit component surfaces surrounding the seal are primarily non-energizing surfaces, which are referred to herein as "non-energizing surfaces." While thenon-energizing surfaces may be engageable with the seal 38 or 52, the seal is typically not compressed by such surfaces, and thus is not energized thereby.

Generally, each seal 38 and 52 is situated in the bit 10 such that it is capable of providing a static seal against an energizing surface of one component at a "static seal interface," the seal 38, 52 generally having little or no relativemovement with that component. The static seal interfaces of seals 38, 52 are identified with the numerals 36 and 37, respectively. The surface of each seal 38, 52 forming the static seal interface is referred to as the "static sealing surface" or"primarily static sealing surface." A dynamic seal is generally formed at a "dynamic sliding seal interface" between the seal 38, 52 and the other energizing surface (of a different bit component) with which the seal 38, 52 primarily engages. Thedynamic sliding seal interfaces of seals 38, 52 are identified with the numerals 45, 54, respectively. The surface of each seal 38, 52 forming the dynamic sliding seal interface is referred to as the "dynamic sealing surface" or "primarily dynamicsealing surface" 44, 55 of the seal 38, 52, respectively, and the energizing surface of the bit component forming the dynamic sliding seal interface is referred to as the "contact surface" 46, 56, respectively. Finally, each seal 38, 52 includesprimarily non-energized surfaces, referred to herein as "non-energized" surfaces, that are engageable with the non-energizing surfaces of the bit components. For example, secondary seal surfaces 308 and 309 of FIG. 17 may be engageable with conenon-energizing surfaces 306, 307. Thus, the term "sealing surfaces" of a seal 38 or 52 as used herein encompasses all such seal surfaces.

Still referring to FIG. 4, while the present invention is not limited to any particular types of primary and secondary seals 38, 52, the primary seal 38 is typically an O-ring seal 43 having a dynamic sealing surface 44 constructed at leastpartially of an elastomeric material (not shown). An example of an O-ring seal useful with the present invention is described in U.S. Pat. No. 5,402,858 to Quantz et al., which is hereby incorporated herein by reference in its entirely. Other typesof O-ring seals as are or become known in the art to be compatible for use as sealed bearing drill bit seals may be used. It should be noted that the term "O-ring" as generally used herein with respect to both the annular primary seal 38 and the annularsecondary seal 52 is not limited to seals having only circular cross-sections, such as seal 43 of FIG. 4, but is intended to include seals having non-circular cross-sections, such as seal 43 of FIG. 5. Other types of annular sealing members (other thanO-ring seals as defined above) that are, or become known to be, compatible for use as primary seal 38 may likewise be used. For example, the primary seal 38 may be a PolyPak.TM., Quad-Ring.RTM., U-Cup.TM., Spring Loaded U-Cup.TM., Lip Seal, SpringLoaded PolyPak.TM., seal. Furthermore, the seal 38 may be constructed of any suitable material or materials as is or becomes known in the art.

Referring to FIGS. 4 and 6, an annular outer, or secondary seal 52 is shown disposed in the bit 10 between the primary seal 38 and the opening 74. It should be noted that the term "secondary seal" as used generally herein includes single elementseals, such as O-ring seals 60 (FIGS. 4, 5) or other types of annular sealing members that are, or become known to be, compatible for use as a secondary seal 52 in a dual-seal drill bit. Further, the seal 52 may be constructed of any suitable materialor materials as is or becomes known in the art.

One or both of the seals 38, 52 may be disposed in grooves formed in bit components, or in interstices formed between bit components. A "groove," such as grooves 85, 98 of FIG. 4, includes a cutout portion in a single bit component. In agroove, at least a portion of each of a pair of opposed non-energizing surfaces are surfaces of a single component. When a seal is disposed in a groove, the seal is at least partially confined in non-energizing directions by primarily non-energizingsurfaces of a single bit component. An "interstice," such as interstice 85a (FIG. 7) and interstice 98a (FIG. 8), is an annular area formed between bit components, wherein no portion of each of any pair of opposed non-energizing surfaces are surfaces ofa single bit component. Further, each of a pair of opposed non-energizing surfaces of an interstice is at least partially on a different bit component.

The placement of one or both seals 38, 52, in interstices 85a, 98a generally occupies less space within the bit 10 as compared to the placement of one or both seals 38, 52 in grooves. Seal arrangements 29 with one or both seal 38, 52 ininterstices can be very compact, allowing, for example, the placement of longer bearings, such as bearings 25a (FIG. 7), in the bearing cavities 75, increasing load capacity. Further, the leg 20 and cone 18 of the bit 10 will generally be stronger thanwhen grooves are formed therein, the formation of grooves requiring removal of mass of the bit component. For example, the use of interstices allows more optimal load capacity of the leg 20 than with the use of grooves, reduces the stress concentrationfactor in the leg 20 resulting from use of a groove formed in the leg 20 and reduces the possibility of breakage of the leg 20 at the groove, thus enhancing bit longevity. The use of interstices also saves time and effort in construction of the bitcomponents, and reduces the complexity of the manufacturing process by eliminating the difficulty in machining grooves into the leg 20, leg journal 23 and cone 18.

Now referring to FIG. 4, the placement of one or both seals 38, 52 in grooves 85, 98, respectively, may provide benefits. For example, the opposing non-energizing surfaces 145 of groove 98 provide stability to the primarily elastomeric,elongated secondary O-ring seal 60. As pressure is applied to the seal 60 by the energizing surfaces 56, 37a of the groove 98, the seal 60 has a natural tendency to deform or bow therebetween. In addition, in a high differential pressure environment,such as a typical petroleum well, as will be described further below, the seals 38, 52 may be subject to being drawn, or extruded, into the annular chamber, or space 100, that is formed between the seals 38, 52. Such deformation and extrusion of a sealcan reduce the sealing effectiveness of the seal and lead to seal failure. The opposing non-energizing surfaces 145 of the groove 98 will provide support for the sides of the seal 60, assisting in preventing such deformation. Furthermore, becauseopposing non-energizing surfaces 145 of groove 98 are both at least partially formed in the same bit component, and because a seal 52 in the groove generally does not move relative to the bit component within which the groove 98 is formed, the seal 52thus being generally stationary relative to such opposing non-energizing surfaces 145, contact between the seal 52 and the non-energizing surfaces 145 that may occur during operations will not subject the seal 52 to substantial shear stress and wear thatwould occur if there was relative movement between the seal 52 and surface 145, which would damage the seal 52. The same benefits typically exist for the primary seal 38 in a groove 85.

The seals 38, 52 may be disposed in any among a variety of configurations of grooves and interstices as is desirable. For example, FIG. 5 shows the primary seal 38 may be disposed in an annular groove 85 formed in the cone 18. A dynamic slidingseal interface 45 is created between a dynamic sealing surface 44 of the primary seal 38 and a contact surface 46 of the journal segment 23 as the seal 38 generally rotates with the cone 18 relative to the leg 20. The primary seal 38 may instead bedisposed in a groove 85 formed in the leg journal segment 23 (FIG. 4). In such configuration, a dynamic sliding seal interface 45 is formed between contact surface 46 of the cone 18 and dynamic sealing surface 44 of the seal 38 as the cone 18 generallyrotates relative to the leg 20 during operations.

The secondary seal 52 may be disposed in a groove 98 formed in the cone 18 (FIGS. 4, 9), the seal 52 generally rotating with the cone 18 relative to the leg 20. A dynamic sliding seal interface 54 is created between the dynamic sealing surface55 of the seal 52 and the contact surface 56 of the leg 20 (FIG. 9), or the contact surface 56 of the leg journal segment 23 (FIG. 4). In another configuration, the secondary seal 52 is disposed in a groove 98 in the journal segment 23, as shown in FIG.5. In yet another configuration, the secondary seal 52 is disposed in a groove 98 in the leg backface 22 (FIG. 6). In each of these configurations, a dynamic sliding seal interface 54 is created between dynamic sealing surface 55 of the seal 52 andcone contact surface 56, the seal 52 being generally stationary relative to the leg 20 as the cone 18 moves relative thereto.

In various configurations, both seals 38, 52 are disposed in grooves. In FIG. 4, for example, the primary seal 38 is disposed in a groove 85 in the journal segment 23, while the secondary seal 52 is disposed in a groove 98 in the cone 18. InFIG. 5, the primary seal 38 is disposed in a groove 85 in the cone 18 and the secondary seal 52 is disposed in a groove 98 in the journal segment 23.

It should be understood, however, that the present invention is not limited any particular location, configuration or placement of the dual-seals in the bit.

As further background, the bit 10 may be configured such that the majority of the forces placed on the secondary seal 52 are either primarily axial, such as shown in FIGS. 3 and 6, or primarily radial, such as shown in FIGS. 4 and 5. As usedherein, "axial" means generally parallel to, or in a plane not intersecting with, the central axis 23a of the journal segment 23 (FIG. 4), while "radial" means in a plane generally perpendicular to the central axis 23a of the journal segment 23.

For explanatory purposes, a secondary seal 52 having primarily radial forces acting on the seal 52 is shown in FIG. 10 disposed between components C, and C.sub.2. Component C.sub.2 has contact surface 56 that engages the dynamic sealing surface55 of the seal 52, and moves relative to component C.sub.1 similar to the relationship of cone 18 (C.sub.2) and journal 23 (C.sub.1) of FIG. 8. Opposing forces F.sub.1 and F.sub.2 from components C.sub.1 and C.sub.2 deflect the seal 52 across the widthW.sub.1 of the seal 52. As used herein, the term "deflection" means a change in the cross-section of a seal from its original shape in a particular direction (axial, radial, other) as the seal is being compressed between two components of a drill bit. "Elastomeric deflection" occurs when the spring force of the seal is caused by primarily elastomeric material of the seal. The forces placed upon the seal 52 are primarily radial because the opposing forces F.sub.1 and F.sub.2 are substantiallyperpendicular to the axis of rotation A of the moving component C.sub.2. In FIG. 11, Component C.sub.2 moves relative to component C.sub.1 similar to the relationship of cone 18 (C.sub.2) and leg 20 (C.sub.1) of FIG. 6. The dynamic sealing surface 55of the seal 52 engages contact surface 56 of component C.sub.2. Opposing forces F.sub.1 and F.sub.2 from components C.sub.1 and C.sub.2 deflect the seal 52 across the width W.sub.2 of the seal 52. Primarily axial forces are placed upon the seal 52because the forces F.sub.1 and F.sub.2 are substantially parallel to the axis of rotation A of the moving component C.sub.2.

The terms "radially energized" and "primarily radially energized" as used herein means that the major component, or majority, of the deflecting forces on a seal are in the radial direction, while "axially energized" and "primarily axiallyenergized" means that that major component of the deflecting forces on a seal are in the axial direction. It should be understood, however, that the primary and secondary seals 38, 52 need not be primarily axially or radially energized, but may begenerally energized axially and radially, or energized in another manner. Generally, a primarily radially energized seal 52, such as shown in FIGS. 4 and 5, experiences less variation in total deflection during operations and thus a more uniform contactpressure profile across the seal's dynamic sealing surface, as compared to an axially energized seal 52 (FIG. 6) because the cone 18 typically experiences less movement, cone cocking or misalignment relative to the leg 20 in the radial direction.

"Contact pressure" as used herein is the amount of pressure between a seal's dynamic or static sealing surface and the energizing surface of the bit component engaged by such seal surface resulting from placement of forces on the seal during itsdeflection. The contact pressure "profile" or "distribution" as used herein means the contact pressure on the seal at each location among numerous locations on the seal's (dynamic or static) sealing surface, while the "peak" contact pressure is thehighest single value of contact pressure anywhere on the sealing surface. It is noteworthy that a more uniform contact pressure profile may result in more optimized and predictable seal operating conditions, reduced wear to the seal 52 and the contactsurface 56, and decreased frictional heat produced thereby. Further, the dynamic sealing surface 55 of a radially energized seal 52 is generally capable of experiencing less lift-off caused by the misalignment, or relative movement, of the cone 18 andleg 20. The value of contact pressure, contact pressure profile or distribution and peak contact pressure may be measured when the drill bit in not in operation, such as upon assembly. During use, or bit operation, these variables are dynamic and theirvalues will change.

For further background, primarily radially energized secondary seals 52 may be positioned between the cone 18 and leg 20, such as shown, for example, in FIG. 12, or between the cone 18 and leg journal segment 23 (FIGS. 4, 16). FIG. 4 depicts theuse of an annular elongated O-ring 60 having a non-circular cross-section as a radially energized secondary seal 52. In FIG. 12, secondary seal 52 is an annular O-ring 60 having a circular cross-section that is primarily radially energized betweensurface 79 of the cone 18 and surface 86 of an annular lip 81 extending from the leg 20. The dynamic sliding seal interface 54 may be created between the outer surface 115 of the O-ring 60 and either, or both, of surfaces 79, 86. Primarily axiallyenergized secondary seals 52 are shown, for example, in FIGS. 6 and 9. When the secondary seal 52 is primarily axially energized in bit 10, the seal 52 must generally be capable of withstanding a wide range of deflection due to the significant end-playof the cone 18 relative to the leg 20.

The present invention provides various apparatuses, techniques and methods for balancing or minimizing the pressure differential across the primary and secondary seals 38, 52. Referring to FIGS. 8 and 13, the annular chamber, or space, 100 isformed between the primary and secondary seals 38, 52 and between the cone 18 and leg 20. The space 100 may be in substantially absolute fluid isolation from the bearing cavity or cavities 75, bearing lubricant systems (not shown), cone bore 73 and bitbearing system 15. The term "substantially absolute fluid isolation" as used herein means a relationship where it is intended that there be no fluid communication, but which may yield some degree of leakage, such as leakage of fluid past the primaryseal during normal operations. Further, an incompressible fluid (not shown), such as grease, may be disposed within space 100, serving as a hydrostatic pressure transmission media and also as a seal lubricant. For example, during drilling in aprimarily liquid circulation fluid drilling environment where a significant hydrostatic head or borehole pressure is anticipated, such as petroleum borehole drilling, the incompressible fluid in space 100 transmits pressure between the bore 73 of thecone 18 or bearing cavity 75, and the exterior 49 of the bit 10 as the internal and external pressures vary during operations. In such instance, if the space 100 is not filled with incompressible fluid, such as grease, the pressure differential couldcause the seals 38, 52 to be drawn to and possibly extruded into the lower pressure space 100. As used herein, the terms "hydrostatic head" and "borehole pressure" mean pressure created by a column of fluid at a specific depth, such as the depth of thedrill bit.

Incompressible fluid may be placed into the annular space 100 by any suitable methods, which may vary depending on the configuration of the present invention. For example, space 100 may be vacuum filled with incompressible fluid through one ormore channels 222 (FIG. 8) accessible from the surface 21 of the leg 20 at least during assembly of the bit 10, such as after the seals 38, 52 are placed into the bit 10 and the leg 20 and cone 18 are connected. Once the space 100 is sufficiently filledwith incompressible fluid, the channel 222 may be filled, or plugged with any suitable type of plug, such as with a threaded plug, welded plug, or a metal plug, 222a, secured in channel 222 by weld, interference fit, or other conventional techniques. Itshould be understood that the channel and plug if used, can take any other form or configuration that is suitable for use with the present invention.

One aspect of the present invention is a preferred incompressible fluid for use between the primary and secondary seals 38, 52. It should be understood, however, that the pressure communication apparatuses, techniques and methods of the presentinvention do not require the inclusion of the preferred incompressible fluid. The preferred incompressible fluid, such as a grease, has the capabilities of retaining sufficient viscosity to act as a medium for the transmission of energy between theprimary and secondary seals and of retaining its lubrication properties when exposed to drilling fluid. For example, with the inclusion of such a preferred incompressible fluid in space 100 of the bit configuration of FIG. 4, the intrusion of drillingfluids into the space 100 from the gap 50 will not cause the incompressible fluid in space 100 to substantially chemically decompose. In effect, the use of an incompressible fluid in accordance with the present invention will assist in ensuring thepresence of lubricant on the outer side of the primary seal 38 and its dynamic sealing surface 45, which can assist in preserving and extending the life of the primary seal 38, and thus preserve the contents of the bearing cavity 75 and the drill bit 10.

In another aspect, the preferred incompressible fluid can be designed to possess the capability of slowing the intrusion of abrasive particles through the space 100 to the primary seal 38. For example, the incompressible fluid, such as a thick,tacky grease, may be designed to be capable of trapping debris particles in the space 100, or causing such particles to become suspended and slowing the formation of conglomerates of such particles. Such grease will act as a barrier to prevent or delaythe ingress of such particles to the primary seal 38, thus assisting in preserving the primary seal 38.

Any suitable composition of incompressible fluid having one or more of the above capabilities may be used. For example, the incompressible fluid could be a composition of all synthetic components or a blend of synthetic and mineral components. For another example, the incompressible fluid may include few, or no, extreme pressure additives or metal-to-metal friction reducers, and/or may include a higher percent by weight of tackifiers as compared to conventional sealed bearing drill bit bearinglubricants, such as disclosed in U.S. Pat. No. 5,589,443 issued on Dec. 31, 1996, having a common assignee as the present application and hereby incorporated by reference in its entirety. For example, the incompressible fluid is preferably a greasepossessing a water washout valve less about than approximately 50%, and more preferably less than about 30%, per ASTM D-4049 water spray test for lubrication characteristics. The grease may also preferably include polymer tackifer of betweenapproximately 1% and 5% by weight. The grease may also preferably be a mineral synthetic blend in which minerals constitute approximately 10-30 percent of the base oil, the balance of approximately 70-90 percent of the base oil being synthetic.

A particular composition of the preferred incompressible fluid includes the following:

In accordance with the present invention, there is provided various techniques and apparatuses for balancing or minimizing the pressure differential across the primary and secondary seals 38, 52 of a dual-seal sealed bearing drill bit. Thepressure communication apparatuses, techniques and methods of the present invention generally involve the migration of fluid from the annular space 100 to the bit exterior 49, and may also include the migration of fluid from the borehole 17 into thespace 100. The objective is to communicate fluid pressure between the space 100 and borehole 17 so that the chamber pressure within the space 100 (FIG. 17) may be maintained equal to or within a reasonable range of the borehole pressure.

All of the various structures described below and variations thereof can be used for at least permitting the flow of fluid from the annular space 100 to the borehole 17, or "one way fluid migration," and, as will become apparent, can be used ormodified to be used for permitting fluid flow in both directions between the space 100 and borehole 17 as "two-way fluid migration" or "biased two-way fluid migration." "Biased two-way fluid migration" allows migration in one direction, such as from thespace 100 to the borehole 17, at lesser differential pressure ranges than migration in the other direction. Furthermore, these structures include structures integral to the seal 52 and/or structure integral to one or more bit components, or acombination thereof.

In one configuration of the present invention, now referring to FIG. 7, the seal arrangement 29 may be configured so that the seals 38, 52, particularly their respective dynamic sealing surfaces, have different contact pressures, contact pressureprofiles and/or peak contact pressures. Using the peak contact pressure as a reference, generally, the lower the peak contact pressure on a seal, the more limited the sealing capability of the seal and the less the seal will wear. The higher the peakcontact pressure, the more sealing the seal will provide and the more the seal will wear and generate heat. Because it is typically desirable that the primary seal 38 generally provide an absolute seal around the bearing cavity 75, the bit 10 isdesigned such that the peak contact pressure on the primary seal 38 is great enough to overcome and resist pressure generated in space 100, referred to herein as the "chamber pressure" of space 100. If the peak contact pressure of the primary seal 38 istoo low, fluid could pass by the seal 38 from the space 100 into the bearing cavity 75, contaminating its contents, such as the bearing system 15.

In accordance with this aspect of the present invention, in some operations, such as drilling in an environment having a significant hydrostatic head, it may be desirable to include a secondary seal 52 with a contact pressure, contact pressureprofile an/or peak contact pressure that is lower than that of the primary seal 38. One reason maybe to allow fluid migration past the secondary seal 52 for pressure communication between the space 100 and bit exterior 49, as will be described furtherbelow. Another reason is to reduce wear on the secondary seal 52.

The contact pressure, contact pressure profile and peak contact pressures of the seals 38, 52 can be affected by controlling or selecting the material composition of the seals 52, 38, which will vary the resistance of the seal to compressionbetween bit components. Differing material compositions are disclosed, for example, in U.S. patent application Ser. No. 08/727,001 filed on Oct. 8, 1996, entitled "Composite Rock Bit Seal," U.S. patent application Ser. No. 08/980,917 entitled"Composite Earth Boring Bit Seal" filed on Dec. 1, 1997, and U.S. Reissue Application Serial No. 08/649,954 entitled "Composite Seal for Rotary Cone Rock Bits" and filed on Jul. 8, 1996, all of which have a common assignee with the present applicationand are hereby incorporated by reference in their entireties.

Another way to vary or control the contact pressure of seals 38, 52 is by shaping the seals 38, 52. Generally, the greater the height of the seal as measured between it's static and dynamic sealing surfaces, the lower the seal's peak contactpressure assuming the same deflection. Referring to FIG. 14, for example, seals 60, 43 could be formed with widths 60a, 43a of 0.250" and seal 60 formed with a height 60c of 0.500." Seal 43, having a circular cross-section, would have a height 43b of0.250". All other variables, such as material composition and seal deflection, being the same for both seals 43, 60, the elongated O-ring seal 60 would have peak contact pressures at its dynamic and static sealing surfaces (not shown) lower than thoseof the seal 43, as long as seal 60 is not restricted in deflection by the sidewalls 145 of groove 98.

Referring again to FIG. 7, the contact pressure on seals 38, 52 could also be controlled or varied by shaping the dynamic sealing surfaces 44, 55 of the seals 38, 52, respectively. All other variable being constant, the larger the area of thedynamic sealing surface of a seal, the lower the contact pressure. The same is true for the static sealing surfaces 36a, 36b of the seals 38, 52, respectively. For example, as shown in FIG. 15, the static sealing surface 36b of seal 60 may be smallerthan its dynamic sealing surface 55, causing the peak contact pressure of the seal 52 to be greater at the static sealing surface 36b than at the dynamic sealing surface 55.

The use of seals having a non-circular cross sections, such as elongated O-ring seal 60 shown in FIG. 13 and elongated O-ring seal 43 of FIG. 8, provides other benefits that may be desirable in various configurations. Generally, all othervariables being equal for two seals having the same deflection, a seal having a non-circular cross-section may require a groove or interstice that is narrower than the groove or interstice necessary to carry a seal having a circular cross-section,allowing more space in the bit for other components, such as bearings 25a, and allowing greater bearing capacity. Referring to FIG. 13, for example, if a deflection of 0.050" is desired for each seal 60, 43 where a 10% squeeze is expected, an O-ringseal 43 having a width of 0.500" would be necessary, requiring a groove 85 of sufficient width 85d to accommodate the seal 43. Because the elongated O-ring seal 60 requires only a width 60a of 0.250" to provide a deflection of 0.050" if the seal 60 hasa height 60c (FIG. 14) of 0.500," the width 98d of the groove 98 would be smaller than the width 85d of the groove 85.

In another aspect of the invention, the contact pressure can be varied between the primarily dynamic sealing surface 55 and the primarily static sealing surface 36b (FIG. 4) of the secondary seal 52 to allow fluid migration past the seal 52. Similar techniques can be used to vary the contact pressure of the static and dynamic sealing surfaces of seal 52 as described above with respect to differing the contact pressure between the dynamic sealing surfaces of the primary and secondary seals38, 52. Further, various of the techniques described below can be used in this type of configuration.

In still another aspect of the present invention, the contact pressure can be varied between circumferentially adjacent regions of one of the sealing surfaces of the secondary seal 52 using the techniques described above and below. This can bedone with the static sealing surface 36b(FIG. 4), dynamic sealing surface 55, and/or possibly even one or more non-energizing surfaces of the seal, or a combination thereof. As used herein, the term "circumferentially adjacent" means next to one anotheron either the outer or the inner circumference of an annular shaped member or area, such as a seal, seal surface, bit component surface, groove and interstice. For example, the dynamic sealing surface at a particular cross-section of an O-ring seal isnot circumferentially adjacent to the static sealing surface at that cross-section of the seal, but is circumferentially adjacent to the dynamic sealing surface at an adjacent cross-section of the seal.

In another aspect of the invention, fluid migration, particularly two-way fluid migration, past the secondary seal 52 may be accomplished by varying the thickness of the secondary seal 52, such as shown for example in FIG. 17. In FIG. 17, anelongated O-ring secondary seal 52 is disposed in groove 98 between the cone 18 and leg journal segment 23. A primarily static seal is formed between the static sealing surface 300 of the seal 52 and the energizing cone surface 302. The seal 52 has atleast one region having a thin portion 304a with a thickness that is smaller than the thickness of the remainder of the seal 52. Referring to FIGS. 17a and 17b, at least one thin portion 304a, such as lip 304, is formed in the seal 52 along the outersurface 300. The surface 300 at the lip 304 is thus thinner than the surface 300 across the adjacent circumferential regions, or remaining circumference, of the seal 52.

The thin portion 304a may take any suitable shape, configuration, orientation and length 303. In FIG. 17b, for example, the thin portion 304a is a lip 304 that is horizontally oriented relative to the outer surface 300 of the seal 52 andpossesses a thickness 305 that is less than the thickness 301 of the seal 52. In FIG. 17c, a lip 304 is shown in the shape of a bellows. Another example is a thin portion that is vertically oriented (not shown) relative to the outer surface 300 of theseal 52. It should be understood that other surfaces of the secondary seal 52, such as the dynamic sealing surface or non-energized surfaces, or a combination thereof may have the one or more regions having thin portions 304a in accordance with thisaspect of the invention.

Referring again to FIG. 17, when the pressure in the space 100 exceeds the borehole pressure, the lip 304 will tend to deform in the direction of the gap 50, allowing the migration or flow of fluid, particularly lubricant (not shown), from thespace 100, past the seal 52, through the gap 50 and to the bit exterior 49. If the pressure in the space 100 is instead lower than the borehole pressure, the lip 304 will tend to move in the direction of the space 100, allowing drilling fluid (notshown) to migrate from the gap 50 into the space 100.

The seal 52 can, if desired, be designed to vary the pressure tolerance of the thin portion(s) 304a to allow fluid migration at a particular differential pressure value or range (between the chamber pressure of the space 100 and the boreholepressure). This can be done, for example, by selecting a particular length 303, thickness 305 and/or material properties of the region(s) of the seal 52 having the thin portion 304a, or of the seal 52 itself. For example, increasing the length 303 ofthe thin portion will lower the stiffness of the thin portion, lowering its pressure tolerance. The seal 52 may thus be designed to allow fluid migration by the secondary seal 52 when the differential pressure is, for example, at a certain value orwithin a certain range, such as between about 0.0 psi to about 100.0 psi, and preferably between about 30 psi and about 70 psi.

Now referring to FIGS. 17a-c, a flow enhancement mechanism 310a involving a different sealing surface or surfaces of the seal 52 (other than the seal surface located on the thin portion 304a) can be included to assist in the migration of fluidpast the secondary seal 52. The flow enhancement mechanism 310a can be integral to the seal 52, and/or to one or more bit component surfaces adjacent the seal 52. For example, referring to FIGS. 17a-c, the flow enhancement mechanism can be a sealsurface feature, such as protrusions 310 on the side (non-energized) surfaces 308, 309 proximate to the thin portion 304a of the seal 52. The protrusions 310 create fluid flow passageways between the side surfaces 308, 309 of the seal 52 and theadjacent non-energizing cone surfaces 306, 307 (FIG. 17) with which they are engageable, respectively. Other examples of seal surface features that can be used to serve as flow enhancement mechanisms 310a include ridges, waves, corrogations (not shown)and any other suitable surface feature known in the art to be capable of creating fluid flow passageways between the seal 52 and adjacent bit component surfaces without substantially surrendering the integrity of the seal 52. Similarly, the flowenhancement mechanism(s) 310a can be formed on a region of one or more bit component surface other than the surface engageable with the thin portion 304a of the seal 52, such as in the form of slits, grooves, depressions, waves, pits, cut-outs, pockets(not shown) and any other suitable surface feature known in the art to create fluid flow passageways between the component surface and the seal 52 without substantially surrendering the integrity of the seal 52 or bit component. In effect, the flowenhancement mechanism 310a, whether integral to the seal or bit component(s), or both, can be any alteration to the subject surface of the seal or bit component in one or more regions of the seal or bit component that render such surface uneven ascompared to circumferencially adjacent regions of the item (seal or bit component).

In another aspect of the invention, fluid migration, particularly two-way fluid migration, past the secondary seal 52 may be accomplished by the use of a secondary seal 52 with one or more regions 312 that have a tapered cross-section, such asshown, for example, in FIGS. 18 and 19. In FIG. 18 tapered region 312 is formed only on the side of the seal 52 having the dynamic sealing surface 55; thus, part of the dynamic sealing surface 55 is on the outer surface of the tapered region 312. Thetapered region 312 may instead be located only on the side of the seal 52 having the static sealing surface 323 (FIG. 19). Yet another configuration includes a tapered region 312 formed around the inner and outer circumference (not shown) of the seal52, thus providing tapered regions 312 on both the static and dynamic sealing surfaces. Further, the tapered region 312 can have any shape as long as it provides the corresponding static or dynamic sealing surface, or both, with a smaller cross-sectionthan circumferentially adjacent regions, or the remaining regions, of such surfaces, or as long as it allows fluid migration at a particular differential pressure valve or range, such as when the inner or outer circumference of the entire seal 52, orboth, is tapered.

Still referring to FIGS. 18 and 19, as the differential pressure between the chamber pressure of the space 100 and the borehole pressure varies, or reaches a predetermined level or range, the tapered region 312 will deform away from the higherpressure side, lowering the contact pressure at the tapered region 312 and allowing fluid migration from the higher pressure side generally similarly as described above with respect to FIGS. 17-17c. Also similarly as described above with respect toFIGS. 17-17c, the seal 52 and tapered portion 312 can be designed to allow for fluid migration at specified differential pressures values or ranges, such as by varying the thickness 318, height 319, length (not shown) or material properties of thetapered region 312, or of the seal 52, or a combination thereof Yet further similarly as described above with respect to FIGS. 17-17c, flow enhancement mechanisms 310a may be included.

In yet another aspect of the invention, referring to FIGS. 20-20d, fluid migration, particularly two-way fluid migration, past the secondary seal 52 may be accomplished by the use of a secondary seal 52 with one or more decreased height regions320 upon which one of the sealing surfaces of the seal 52 extends. For example, seal 52 of FIGS. 20 and 20a has decreased height region 320 formed across length 321 of the outer circumference of the seal 52. The static sealing surface 323 of seal 52 isthus on the surface 322 of the decreased height region 320. As shown in FIGS. 20c-d, region 320 has a height 324 which is smaller than the height 326 of the reminder of the seal 52 (the circumferencially adjacent regions of the seal 52), and will thushave a lower contact pressure at static seal interface 37 (FIG. 20).

The decreased height region 320 of the seal 52 can be formed on the side of the seal 52 having the static or dynamic seal surface, or both, and can have any suitable size and configuration, as desired, so long as the sealing surface on the region320 has a contact pressure range lower than the remainder of the seal surface or allows fluid migration at a particular differential pressure valve or range, and the integrity of the seal 52 is not substantially diminished. For example, the region 320can be on the inner circumference of the seal 52 and the region 320 can carry the seal's dynamic sealing surface. For another example, the surface 322 of region 320 can be formed in a concave shape, as shown in FIG. 20b. In use, when the differentialpressure between the chamber pressure of the space 100 (FIG. 20) and the borehole pressure reaches a certain level or range, the contact pressure of the region 320 will be insufficient to retain the fluid pressure and will allow fluid migration from theside with the higher pressure into or out of the space 100. Again, as described above for FIGS. 17-17c, the seal 52 having a decreased height region 320 can be designed to allow for fluid migration at specified differential pressures values or ranges,such as by varying the height 324, length 321 or material properties of the region 320 or seal 52, or a combination thereof. Yet further similarly as described above with respect to FIGS. 17-17c, flow enhancement mechanisms 310a may be included.

Now referring to FIGS. 21-21b, still another aspect of the invention allows two-way fluid migration past the secondary seal 52 with the placement of the seal 52 in a groove 98 or an interstice (not shown) having at least one wide region 330. Thewidth 330g (FIG. 21) of the region 330 is greater than the width 98g of circumferentially adjacent regions, or the remainder, of the groove 98 (or interstice). When the differential pressure across the secondary seal 52 changes or reaches apredetermined level or range, the portion 52h (FIG. 21b) of the seal 52 disposed in the groove 98 (or interstice) at the wide region 330 will be pushed away from the side with the higher pressure, either toward the space 100 or the gap 50, and will moveor twist, allowing fluid passage in that direction.

The wide region 330 can take any suitable shape and form with any desirable width 330g and length 330e (FIG. 21a), such as to cause fluid migration by the secondary seal 52 at a desired pressure differential value or range. In the embodiment ofFIGS. 21-21b, the wide region 330 is created by first and second pockets 331 formed in the non-energizing cone surfaces of the groove 98. Further, as described above with respect to FIG. 17, the seal 52 can be selected to allow for fluid migration atspecified differential pressures values or ranges, such as by varying one or more dimensions, or the material properties, of the seal 52. Yet further similarly as described above with respect to FIGS. 17-17c, flow enhancement mechanisms 310a may beincluded.

In another aspect of the invention, referring to FIGS. 22-24, two-way fluid migration by the secondary seal 52 may be accomplished by altering one or more regions 340a of one or more of the sealing surfaces of the seal 52, such as the dynamicsealing surface 55 (FIG. 22), the static sealing surface 36b (FIG. 23) and/or one or both of the non-energized surfaces (not shown). The sealing surface in the region 340a may be altered in any suitable manner to allow fluid migration by the seal 52 atthe altered region(s) 340a. For example, the altered regions of the seal 52 in FIGS. 22-24 have a plurality of depressions 340 in the subject sealing surface. In FIGS. 22 and 24, the depression 340 are in the dynamic sealing surface 55 of the seal 52,while FIG. 23 shows depression 340 in the static sealing surface 36b of the seal 52. The seal 52 of FIG. 23 could be used, for example, in the dual-seal orientation of FIG. 20. The contact pressure at each depression 340 is lowered (or zero) such thatfluid flows past the seal 52 at the depressions 340 at a certain differential pressure, and can, if desired, be designed to allow migration when there is no differential pressure. Other examples of ways to alter the sealing surface in the altered region340a include forming cut-outs, slits, grooves, pits or any other suitable surface feature or manner of making the sealing surface in the altered region 340auneven as compared to circumferentially adjacent regions, or the remainder, of the sealing surfaceto allows fluid migration by the seal 52 without substantially sacrificing the integrity of the seal.

The altered region 340a can be formed such that fluid will flow past the seal 52 at a predetermined value or range of differential pressure. For example, referring to FIG. 22a, the length 340g and depth 342 of the altered region 340a can beselected for such fluid flow as may be desired. A depression depth 342 of 0.005 inches of the embodiment of FIG. 22a, for example, will possess a lower leak rate than a depression 340 having a depth of 0.025 inches. As shown in FIGS. 22 and 23,depressions 340 can be angled relative to a vertical axis 344 through the seal 52. In the preferred embodiment, these depressions 340 are formed at angles A.sub.1 of between approximately 0 degrees and approximately 60 degrees relative to the centralaxis 344 to allow a desired two-way fluid migration by the seal 52. For yet other examples, the quantity and configuration of surface features or cut-outs of the altered region 340a, such as the depressions 340, can be varied as desired to effect thefluid bypass rate of the seal 52 or for other reasons. An example of a seal 52 having depressions 340 with a non-linear shape is shown in FIG. 24. Further, as described above with respect to FIG. 17, the seal 52 can be selected to allow for fluidmigration at specified differential pressures values or ranges, such as by varying one or more dimensions, or the material properties, of the seal 52 in the altered region 340a, the seal 52 or a combination thereof. Similarly as described above withrespect to FIGS. 17-17c, flow enhancement mechanisms 310a may be included.

Alternately, or additionally, one or more of the energizing and non-energizing surfaces of the bit components surrounding (and engageable) with the seal 52 can be formed with one or more altered regions (not shown) similarly designed as describedabove with respect to the altered regions 340a of the seal 52, to allow fluid migration by the secondary seal 52. Thus, the above two-paragraph description regarding altered regions 340a of the seal 52 can be modified by one of ordinary skill in the artto instead apply to one or more of the bit component surfaces surrounding the seal 52.

Now referring to FIGS. 25-25b, still another aspect of the invention allows fluid migration, particularly two-way fluid migration, past the secondary seal 52 with the placement of the seal 52 in a groove 98 or an interstice (not shown) having atleast one deep region 350a. The sealing surface (such as static sealing surface 36a and dynamic sealing surface 55 in FIG. 25) of the seal 52 disposed in the groove 98 (or interstice) at the deep region 350a will have a lower contact pressure than thesealing surface on unaltered circumferentially adjacent regions of the seal 52. Thus, when the differential pressure across the secondary seal 52 changes or reaches a predetermined level or range, the lower contact pressure of the sealing surface(s) ofthe seal 52 at the deep region 350a will allow fluid passage away from the side having the higher pressure and into the space 100 or gap 50, accordingly.

The deep region 350a can take any suitable or desirable shape, form and configuration with any desirable length 356 and difference in depth 354 from the depth of circumferentially adjacent non-altered regions of the groove 98 (or interstice) asto cause fluid migration by the secondary seal 52 at a desired pressure differential value or range. In the embodiment of FIGS. 25-25b, the deep region 350a is an indent, or cut-out, 350 formed in energizing cone surface 302 of the groove 98. Further,similarly as described above with respect to FIG. 17, the seal 52 can be selected to allow for fluid migration at specified differential pressures values or ranges, such as by varying one or more dimensions, or the material properties of the seal 52 inthe deep region 350a, the seal 52, or a combination thereof. Yet further similarly as described above with respect to FIGS. 17-17c, flow enhancement mechanisms 310a may be included.

In yet another aspect of the invention, referring to FIGS. 26 and 26a, fluid migration, particularly two-way fluid migration by the secondary seal 52 can be accomplished by including a porous inlay 360 in at least a portion of one of the sealingsurfaces of the seal 52. The porous inlay 360, which can be formed, for example, on the dynamic sealing surface 55, the static sealing surface (not shown) or both surfaces, and may extend into the thickness of the seal 52 to (FIG. 26a), serves as amigration path for fluid past the seal 52. In the example of FIG. 26, the porous inlay 360 is disposed in a portion of the dynamic sealing surface 55 of the seal 52, which will allow fluid to migrate in the direction away from the side with the higherpressure at a lower differential pressure than the adjacent or unaltered regions of the sealing surface 55. If desired, the seal 52 with porous inlay 360 can also be designed to allow fluid migration in either or both directions when there is nodifferential pressure.

The size, shape, orientation, location and material composition of the inlay 360 may be selected as desired to allow a particular migration rate, or for other reasons. Examples of materials useful as inlay 360 are wire mesh or screen, fabric,felt or other primarily non-elastomeric material. In FIGS. 26 and 26a, the inlay 360 is constructed of fabric, and is embedded into the seal 52 at a depth of 360b along a length 360c of the dynamic sealing surface 55 of the seal 52. As described abovewith respect to FIG. 17, the seal 52 can be selected to further allow for fluid migration at specified differential pressures values or ranges, such as by varying one or more dimensions, or the material properties of the seal 52, or a combinationthereof. Similarly as described above with respect to FIGS. 17-17c, flow enhancement mechanisms 310a may also be included.

Now referring to FIGS. 27-27c, in another aspect of the invention, the chamber pressure within the space 100 may be maintained equal to or within a reasonable range of the borehole pressure (not shown) by providing for two-way fluid migrationbetween the space 100 and the bit exterior 49. One technique for achieving this is with the inclusion of one or more passages, or conduits, 370 extending between the space 100 and the bit exterior 49. The conduit 370 allows fluid communication betweenthe space 100 and borehole (not shown) or bit exterior 49 by allowing the flow of incompressible fluid from the space 100 to the bit exterior 49 in one direction, and the flow of drilling fluid from the bit exterior 49 into the conduit 370 in the otherdirection, depending on the pressure differential.

In the example of FIG. 27, the conduit 370 extends from the space 100 to an opening 20b in the leg surface 20a and is filled with incompressible fluid (not shown), such as the preferred composition as described above. Referring to FIG. 27c, theconduit 370 may be in direct fluid communication with the borehole and thus exposed to the bit exterior 49. The use of viscous, tacky grease, such as the preferred composition of incompressible fluid, acts as a barrier to the substantial ingress oflarge particles from the bit exterior 49 to the space 100 and primary seal 38. Further, the bit 10 can be designed with the conduit 370 extending to one or more counterbores 371, 372 formed into the leg 20 around the opening 20b. The conduit 370 andcounterbores 371, 372 (if included) may take any suitable shape and configuration. For example, in the exemplary embodiment of FIG. 27, the conduit 370, and counterbores 371, 372 engage the leg 20 at an angle of over about 0 degrees and less than about90 degrees relative to the leg surface 20a. It should be understood that the conduit 370 can extend to an opening 20b on any surface of the leg 20, such as the side surface of the leg 20 indicated in FIG. 25.

Fluid migration through the conduit 370 may be controlled with the inclusion of a fluid control member 374, which may take any suitable form or configuration as desired to allow the fluid migration at a particular rate or range. For example, thecontrol member 374 of FIG. 27 is a perforated washer 376, while the member 374 of FIG. 27b is a filter 378. The fluid control member 374 may further be designed to prevent the ingress of large particles into the conduit(s) 370 from the bit exterior 49.

The washer 376 of FIG. 27 includes one or more perforations 380, which may be sized to control fluid migration or pressure relief at a predetermined range of differential pressure. The washer 376 can be made of a flexible material such as anelastomer, wherein the perforations 380 can be optimized to relieve at a given differential pressure range. In FIG. 27a, for example, the washer 376 has a single perforation 380 in the shape of a slit. The filter 378 of FIG. 27b may be constructed ofany suitable material, such as wire, fiber or felt. Further, a plug 384 having an internal cavity, may be secured in the either or both counterbores 371, 372, such as by interference fit, welding, or threads, for various purposes, such as to secure thecontrol member 374 and conduit 370. It should be understood that the control member 374 can take other forms and configurations, such as any among various suitable one-way and two-way valves known in the art and suitable for use in accordance with thepresent invention. Further, as described above with respect to FIG. 17, the seal 52 can be selected to further allow for fluid migration at specified differential pressures values or ranges, such as by varying one or more dimensions, or the materialproperties of the seal 52, or a combination thereof. Similarly as described above with respect to FIGS. 17-17c, flow enhancement mechanisms 310a may also be included.

The above aspects and configurations of the present invention may be modified by one of ordinary skill in the art to enable "substantially one-way fluid migration" or "biased two-way fluid migration." "Substantially one-way fluid migration" ismigration in one direction with residual, nominal, or normal leakage, migration or backflow in the other direction. "Biased two-way fluid migration" allows migration in one direction, such as from the space 100 to the borehole 17, at a lesserdifferential pressure or range than migration in the other direction. The bit 10 may thus be designed so that fluid migrates from the space 100 to the gap 50 when the pressure differential caused by a higher chamber pressure in the space 100 is within acertain range, and fluid migration from the gap 50 to the space 100 for a greater pressure differential caused by higher borehole pressure than in the space 100, or vise versa, as desired.

Biased two-way fluid migration or substantially one-way fluid migration may be achieved, for example, by modifying the geometry of the bit component surfaces surrounding the seal 52, or by modifying the seal 52. In one configuration, referringto the embodiment of FIGS. 28-28b, at least one of the bit components surfaces surrounding the seal 52 of the groove or interstice within which the seal 52 is disposed includes at least one wide region 391, or is otherwise uneven with respect tocircumferentially adjacent regions of the bit component surface.

In the example of FIGS. 28-28b, the outermost primarily non-energizing surface 306 surrounding the secondary seal 52 includes one or more wide regions 390 adjacent the primarily non-energized side 308 of the seal 52. The wide region 391 is apocket, or cut out, 390 formed in the cone 18, thus extending the width of the groove 98 at the wide region 391 by the width 394 of the pocket 390. When the chamber pressure in the space 100 exceeds the pressure in the borehole (not shown) or bitexterior 49, such as within a certain predetermined range, the portion of the seal 52 disposed in the groove 98 at the wide region 391 will be drawn toward the gap 50 and will move, twist, or otherwise yield, allowing the passage of fluid from the space100 to the gap 50. A higher differential pressure (where the borehole pressure exceeds the chamber pressure) will be necessary to cause the seal 52 to allow migration of fluid in the opposite direction, if at all.

The wide, or uneven, region 391 can take any shape, form or configuration as desired, and the length 392 and width 394 of the wide region 391, or pocket 390 of FIG. 28, can be selected to allow fluid migration by the seal 52 within specificdifferential pressure ranges, if desired. Further, as described above with respect to FIG. 17, the seal 52 can also be selected to allow for fluid migration at specified differential pressures values or ranges, such as by varying one or more dimensions,or the material properties of the seal 52 in the wide region 390, in the seal 52 or a combination thereof Yet further similarly as described above with respect to FIGS. 17-17c, flow enhancement mechanisms 310a may be included.

In another aspect of the present invention, referring to FIG. 29, the seal 52 can be modified to allow biased two-way fluid migration, or substantially one-way fluid migration, by the secondary seal 52. The seal 52 can be modified to allow suchmigration past the static 323 or dynamic 55 sealing surfaces, the non-energizing surfaces, or a combination thereof, and regardless of whether the seal 52 is in a groove 98 or interstice (not shown). In the example of FIG. 29, the seal 52 is shownlocated in groove 98 in the cone 18 and having an at least partially non-symmetrical cross-sectional region 406a upon which a portion of the dynamic sealing surface 55 is formed. It should be understood that there can be one or numerous such regions406a, or the entire seal 52 can have an at least partially or fully non-symmetrical cross-section. The surface 55 has a contact width 400 smaller than the width 402 of the seal 52 (as well as the width of the circumferentially adjacent regions of thedynamic sealing surface 55). When the differential pressure on the seal 52 falls within a certain range, the contacting portion 404 of the seal will deform into the body 406 of the seal 52, move within the groove 98, or otherwise yield, allowing fluidmigration by the seal 52.

Still referring to the example FIG. 29, the non-symmetrical region 406a of the seal 52 is oriented or shaped such it is not symmetrical relative to the seal axis 524. As a result, the contacting portion 404 of the seal 52 is off-center, orproximate to the gap 50. Thus, the distance from the contacting portion 404 to the gap 50 in FIG. 29 is smaller than the distance from the contacting portion 404 to the space 100. With this type of configuration, the differential pressure caused byhigher chamber pressure in the space 100 sufficient to cause fluid migration from the space 100 to the gap 50 will be lower than the differential pressure caused by higher borehole pressure necessary to cause fluid migration into the space 100 from thegap 50. Further, as described above with respect to FIG. 17, the seal 52 can be selected to further allow for fluid. migration at specified differential pressures values or ranges, such as by varying one or more dimensions, or the material propertiesof the seal 52, or a combination thereof. Similarly as described above with respect to FIGS. 17-17c, flow enhancement mechanisms 310a may also be included.

In yet another aspect of the invention, biased two-way fluid migration, or substantially one-way fluid migration from the space 100 to the bit exterior 49 can be achieved with the use of a conduit 370, such as the conduit 370 of FIG. 27, but alsoincluding a primarily one-way valve. For example, the embodiment of FIG. 30 includes a one-way valve 410 of any suitable form in fluid communication with the conduit 370 and bit exterior 49. One type of valve 410 includes a ball 414 and biasing member419, such as a spring 420, disposed in a counterbore 371. The spring 420 biases the ball 414 against the conduit opening 422. When the pressure in the space 100 and conduit 370 reach a sufficient level higher than the borehole pressure, the ball 414 ispushed into the counterbore 371, compressing the spring 420 and allowing fluid flow from the conduit 370 to the borehole, or bit exterior 49. The ball 414 and spring 420 may be secured in the counterbore 371 with a plug 384 having an internal cavity384b and openings 384a, 384c to allow the flow of fluid therethrough. The valve 410 can be designed to disallow migration of fluid in the other direction, or to allow such fluid migration at a particular differential pressure value or range. It shouldbe understood that the one-way valve 410 and passage 310 configuration can take any other suitable form. Further, as described above with respect to FIG. 17, the seal 52 can be selected to further allow for fluid migration at specified differentialpressures values or ranges, such as by varying one or more dimensions, or the material properties of the seal 52, or a combination thereof. Similarly as described above with respect to FIGS. 17-17c, flow enhancement mechanisms 310a may also be included.

Biased two-way fluid migration or substantially one-way fluid migration may be useful, for example, in drilling conditions where it is desired to minimize the ingress of particles, debris or fluid from the bit exterior 49 to the space 100 orprimary seal 38. Further, biased two-way fluid migration configurations may be used in combination with other pressure communication mechanisms. For example, the example of FIGS. 28-28b, can be used in conjunction with a pressure relief conduit 370such as shown in FIGS. 27-27c, or a primarily one-way pressure relief conduit (not shown) that primarily allows the flow of drilling fluid into the bit 10.

Each of the foregoing aspects and features of the invention may be used alone or in combination with other such aspects and features. For example, two substantially one-way fluid migration mechanisms can be used to achieve two-way fluidmigration, as well as with other pressure communication techniques and mechanisms that are or become known in the art. For another example, flow enhancement mechanisms as described with respect to FIG. 17 can be used with any above aspect. Theembodiments described herein are exemplary only and are not limiting of the claimed invention, and modifications thereof can be made by one skilled in the art without departing from the spirit or teachings of this invention. For example, with respect tothe aspects of the invention involving the migration of fluid by the secondary seal 52, various additional factors, such as the material properties of the seal 52, can be selected to effect the ability of the seal 52 to allow fluid migration. Further,each of the above aspects of the invention can be used regardless of the direction of energization of the secondary seal 52, are applicable to the static and dynamic sealing surfaces of the seal 52, are applicable when the seal 52 is in a groove in thecone 18, leg 20 or leg journal segment 23, or in an interstice, and can be used on or in connection with one or more portions of the seal 52, or around the entire circumference of the seal 52. Many variations and modifications of the embodimentsdescribed herein are thus possible and within the scope of the invention. Accordingly, the scope of protection is not limited to the embodiments described herein.